全文获取类型
收费全文 | 59639篇 |
免费 | 2108篇 |
国内免费 | 124篇 |
专业分类
化学 | 37462篇 |
晶体学 | 395篇 |
力学 | 1100篇 |
综合类 | 2篇 |
数学 | 9987篇 |
物理学 | 10914篇 |
无线电 | 2011篇 |
出版年
2023年 | 441篇 |
2022年 | 513篇 |
2021年 | 838篇 |
2020年 | 947篇 |
2019年 | 880篇 |
2018年 | 1606篇 |
2017年 | 1369篇 |
2016年 | 2149篇 |
2015年 | 1664篇 |
2014年 | 1787篇 |
2013年 | 3772篇 |
2012年 | 3827篇 |
2011年 | 3986篇 |
2010年 | 2435篇 |
2009年 | 2160篇 |
2008年 | 3444篇 |
2007年 | 3438篇 |
2006年 | 3070篇 |
2005年 | 2792篇 |
2004年 | 2337篇 |
2003年 | 1890篇 |
2002年 | 1641篇 |
2001年 | 1255篇 |
2000年 | 1166篇 |
1999年 | 858篇 |
1998年 | 623篇 |
1997年 | 550篇 |
1996年 | 708篇 |
1995年 | 500篇 |
1994年 | 545篇 |
1993年 | 531篇 |
1992年 | 498篇 |
1991年 | 404篇 |
1990年 | 395篇 |
1989年 | 355篇 |
1988年 | 312篇 |
1987年 | 320篇 |
1986年 | 305篇 |
1985年 | 438篇 |
1984年 | 423篇 |
1983年 | 311篇 |
1982年 | 318篇 |
1981年 | 324篇 |
1980年 | 276篇 |
1979年 | 254篇 |
1978年 | 251篇 |
1977年 | 237篇 |
1976年 | 219篇 |
1975年 | 200篇 |
1973年 | 208篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
The physico-chemical properties and reactivity tested by hydrogen reduction have been studied for two series of NiO-ZnO mixed oxides of various composition. The solid nickel oxide or zinc oxide in interaction with the solution of nitrate of the second component were used as the precursors in each series. The differences in some physico-chemical parameters of the samples in both series were correlated with their reduction behaviour, followed both in iso- and non-isothermal regime. Moreower, the influence of various factors modifying the reactivity of mixed oxides was also investigated and the results were compared with those obtained from earlier studied analogous systems of quite different origin.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
93.
G. Romero L. Alvarez E. Alanís L. Nallim R. Grossi 《Optics and Lasers in Engineering》2003,40(1-2):81-90
Real-time electronic speckle pattern interferometry (ESPI) was used for tuning and visualization of natural frequencies of a trapezoidal plate. The plate was excited to resonant vibration by a sinusoidal acoustical source, which provided a continuous range of audio frequencies. Fringe patterns produced during the time-average recording of the vibrating plate—corresponding to several resonant frequencies—were registered. From these interferograms, calculations of vibrational amplitudes by means of zero-order Bessel functions were performed in some particular cases. The system was also studied analytically. The analytical approach developed is based on the Rayleigh–Ritz method and on the use of non-orthogonal right triangular co-ordinates. The deflection of the plate is approximated by a set of beam characteristic orthogonal polynomials generated by using the Gram–Schmidt procedure. A high degree of correlation between computational analysis and experimental results was observed. 相似文献
94.
Erzs bet Ill s Etelka Tomb cz 《Colloids and surfaces. A, Physicochemical and engineering aspects》2003,230(1-3):99-109
The ionic strength dependence of humic acid (HA) adsorption on magnetite (Fe3O4) was investigated at pH 5, 8 and 9, where variable charged magnetite is positive, neutral and negative, respectively. The adsorption studies revealed that HA has high affinity to magnetite surface especially at lower pH, where interacting partners have opposite charges. However, in spite of electrostatic repulsion at pH 9 notable amounts of humate are adsorbed. Increasing ionic strength enhances HA adsorption at each pH due to charge screening. The dominant interaction is probably a ligand-exchange reaction, nevertheless the Coulombic contribution to the organic matter accumulation on oxide surface is also significant under acidic condition. The results from size exclusion chromatography demonstrate that the smaller size HA fractions enriched with functional groups are adsorbed preferentially on the surface of magnetite at pH 8 in dilute NaCl solution. 相似文献
95.
M. C. Caracoche J. A. Martínez P. C. Rivas M. A. Taylor A. F. Pasquevich S. Barolin O. A. de Sanctis 《Hyperfine Interactions》2007,179(1-3):87-93
The hyperfine quadrupole interaction at Hf sites in films and powders of 14 mol% CaO–HfO2 and 20 mol% CaO–HfO2 has been determined as a function of temperature. Results indicate the formation of a cubic solid solution and other microstructures assigned to the ?1 (CaHf4O9) and ?2 (Ca6Hf19O44) phases. Dynamical effects on the electric field gradient reveal the existence of oxygen vacancies movements in the solid solution. The thermal behavior of the relaxation constant observed in films allowed the determination of activation energies of 0.54 eV and 0.70 eV for the 14 mol% and 20 mol% CaO doped hafnias, respectively. The influence of the microdomains and the stability of the cubic solid solution are discussed. 相似文献
96.
José A. Anquela Teresa Cortés Miguel Gómez-Lozano Mercedes Siles-Molina 《Acta Mathematica Hungarica》2004,103(3):177-196
We investigate the basic properties of the different socles that can be considered in not necessarily semiprime associative
systems. Among other things, we show that the socle defined as the sum of minimal (or minimal and trivial) inner ideals is
always an ideal. When trivial inner ideals are included, this inner socle contains the socles defined in terms of minimal
left or right ideals.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
97.
Mátyás Bognár 《Acta Mathematica Hungarica》2004,102(1-2):37-84
The following generalization of the Hahn-Mazurkiewicz theorem is proved: Let (E,e) be a locally compact locally connected metric space. Let M be a continuum in this space and let d,e∈ M. Then there is a continuous mapping f: [0,1]→E such that f(0) = d, f(1)= e and M⊂f([0,1]). Also some corollaries of this theorem are proved. 相似文献
98.
B. G. Konopelchenko L. Martínez Alonso E. Medina 《Theoretical and Mathematical Physics》2007,151(3):820-830
Based on the Lenard relations, we completely classify integrable deformations of general algebraic curves. We construct the
general solution of the Lenard relation from the invariance condition with respect to an element of the Galois group of the
curve. We give some examples and also some associated conservation laws.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 151, No. 3, pp. 458–469, June, 2007. 相似文献
99.
We derive the incompressible and compressible k–ε model for locally homogeneous turbulence. The model is rigorously derived on formal mathematical grounds using the MPP modelling technique. This lets us calculate by either analytical or numerical means the closure constants of the model. To cite this article: T. Chacón Rebollo, D. Franco Coronil, C. R. Acad. Sci. Paris, Ser. I 337 (2003). 相似文献
100.
We consider toy cosmological models in which a classical, homogeneous, spinor field provides a dominant or sub-dominant contribution to the energy-momentum tensor of a flat Friedmann-Robertson-Walker universe. We find that, if such a field were to exist, appropriate choices of the spinor self-interaction would generate a rich variety of behaviors, quite different from their widely studied scalar field counterparts. We first discuss solutions that incorporate a stage of cosmic inflation and estimate the primordial spectrum of density perturbations seeded during such a stage. Inflation driven by a spinor field turns out to be unappealing as it leads to a blue spectrum of perturbations and requires considerable fine-tuning of parameters. We next find that, for simple, quartic spinor self-interactions, non-singular cyclic cosmologies exist with reasonable parameter choices. These solutions might eventually be incorporated into a successful past- and future-eternal cosmological model free of singularities. In an Appendix, we discuss the classical treatment of spinors and argue that certain quantum systems might be approximated in terms of such fields. 相似文献